Conventionally, a so-called multifuel internal combustion engine which is driven using a plurality of kinds of fuel having different properties is known. For example, Patent Document 1 discloses a multifuel internal combustion engine which is driven using mixed fuel of gasoline and light oil. In the multifuel internal combustion engine, when the engine starts, the mixing ratio of light oil having high ignitability is increased, and the engine is driven in a diffusion combustion manner. When a smoke discharging amount is large or knocking is generated, a mixing ratio of gasoline having high smoke suppressing effect and anti-knocking effect is increased, and the engine is driven in a premixed combustion manner. Patent Document 2 discloses a multifuel internal combustion engine which can be driven using fuel selected by a driver from many kinds of fuel such as gasoline, light oil and ethanol. Patent Document 2 also describes a multifuel internal combustion engine which is driven in a spark-ignition mode when the engine load is smaller than a predetermined load, and which is driven in a compression hypergolic diffusion combustion mode when the engine load is large. As the ignitability of used fuel is higher, the driving region in the compression hypergolic diffusion combustion mode is enlarged.
Patent Document 1: Japanese Patent Application Laid-open No. 9-68061
Patent Document 2: Japanese Patent Application Laid-open No. 2004-245126